Energy Efficiency Tips for Homeowners

AI Thread Summary
The discussion focuses on calculating the number of active cesium nuclei in an 800-gram fish caught near the Fukushima nuclear power plant, which contains 7.4 megabecquerels of radioactive cesium-137. It highlights that the equation for activity (A(t)) is not suitable for this specific question without proper adjustments for elapsed time. The half-life of cesium-137 is approximately 30 years, but the calculations mistakenly assume a decay period of one year, which is inappropriate since the fish would spoil by then. Additionally, there is a mismatch in units, as the half-life in years was incorrectly applied in an equation where activity is measured in disintegrations per second. Accurate calculations require consistent units and appropriate time frames.
tomcajot
Messages
1
Reaction score
0
Homework Statement
Near the Fukushíma nuclear power plant, a fish was caught with a record amount of radioactive 137-Cs of 7.4 megabecquerels per kilogram. Calculate the number of active cesium nuclei in an 800 gram fish.
Relevant Equations
(Don't know how to add LaTeX, the relevant equations will be in the picture in the solution attempt)
Screenshot 2021-12-08 at 17.34.30.png
 
Physics news on Phys.org
tomcajot said:
Homework Statement:: Near the Fukushíma nuclear power plant, a fish was caught with a record amount of radioactive 137-Cs of 7.4 megabecquerels per kilogram. Calculate the number of active cesium nuclei in an 800 gram fish.
Relevant Equations:: (Don't know how to add LaTeX, the relevant equations will be in the picture in the solution attempt)

View attachment 293787
Hi @tomcajot and welcome to PF.

Here are some points to consider…

Your equation for A(t) is used to find the activity after a given time (t) has elapsed. This isn’t really appropriate in this question (Though the equation can be used if you realize what value to use for elapsed time.)

You have used ‘30’ as the half-life of Cs-137. This is the approximate half-life of Cs-137 in years, Your working implies that you have take t=1 year – i.e. you have assumed the sample has been decaying for 1 year. (The fish will have gone off by then.)

You have also used the half-life in years in an equation where the activity is in Bq (disintegrations per second). So you have a problem with mismatched units.
 
Thread 'Minimum mass of a block'
Here we know that if block B is going to move up or just be at the verge of moving up ##Mg \sin \theta ## will act downwards and maximum static friction will act downwards ## \mu Mg \cos \theta ## Now what im confused by is how will we know " how quickly" block B reaches its maximum static friction value without any numbers, the suggested solution says that when block A is at its maximum extension, then block B will start to move up but with a certain set of values couldn't block A reach...
TL;DR Summary: Find Electric field due to charges between 2 parallel infinite planes using Gauss law at any point Here's the diagram. We have a uniform p (rho) density of charges between 2 infinite planes in the cartesian coordinates system. I used a cube of thickness a that spans from z=-a/2 to z=a/2 as a Gaussian surface, each side of the cube has area A. I know that the field depends only on z since there is translational invariance in x and y directions because the planes are...
Thread 'Calculation of Tensile Forces in Piston-Type Water-Lifting Devices at Elevated Locations'
Figure 1 Overall Structure Diagram Figure 2: Top view of the piston when it is cylindrical A circular opening is created at a height of 5 meters above the water surface. Inside this opening is a sleeve-type piston with a cross-sectional area of 1 square meter. The piston is pulled to the right at a constant speed. The pulling force is(Figure 2): F = ρshg = 1000 × 1 × 5 × 10 = 50,000 N. Figure 3: Modifying the structure to incorporate a fixed internal piston When I modify the piston...
Back
Top